Anxiety?

This is my first post, so bare with me ,,, my son is 7 months old and with in the past month he has a screaming fit for about 10 minutes anywhere between 3-4pm while being watched by DH. I returned to work when he was 4 months old full time, but work 12 hour shifts, so I'm off during the week and DH has him on weekends that I work (the grandmas watch him while I'm working during the week). Neither of us can figure out what the source is. I leave for work while he's asleep, so I don't think it's separation anxiety. It's getting to the point that DH dreads early afternoons on his weekends off. So by the time I get home from working a 12 (or sometimes 16) hour shift, DH is so spent he passes the baby off for his own sanity and I don't get any down time after work... My son has only done this with me twice and that was calmed down in under a minute. We have found that if DH brings our son for a visit on my lunch break where I feed and play with him, things do seem to go smoother.

 He's an all around happy baby with no medical conditions and is breast fed and gets cereal in the evenings now. We tried cereal in the afternoon and it did not go well, lol. Has anyone else experienced this? Any ideas? Thanks a lot, it's always good to use the wisdom of other moms!